Dimensional tolerances are important on a paver’s structural efficiency. Rectangular and shaped blocks need to be designed to include their surrounding space; and their length to width ratio depends upon the final laying pattern. To optimize the block surfacing structural efficiency then every block must be specified and controlled within strict tolerances.

A specification has to cover the quality of the block materials to ensure their long term durability, retention of adequate slip and skid resistance, but also consistency of their physical dimensions and uniformity of shape.

Stress caused by blocks being too close together, resulting in movement from horizontal forces, is minimized by chamfered edges which provide a "cushion" between the blocks.

The ideal joint range is between 2 and 5mm. The space of a joint should cater for dimensional tolerances, deviations in layering, arising for the laying pattern and possibly the setting-out of edge restraints. If joint widths exceed 5mm then the structural ability of surfacing decreases.

Figure 1: Typical Space Arrangement on Rectangular Blocks

Figure 2: Effect of Uniform Spacers on Joint Width

Figure 3: Complex Shaped Block in Herringbone Pattern

Figure 1: Nowadays, spacers are formed on almost every concrete block that is rectangular in shape. They are included to secure a joint space between adjacent blocks, and as mentioned before these spacers ensure a minimum joint width of 1.5-2mm.

Figure 2: The bond shown is a herringbone pattern, in which rectangular blocks are laid in a combination of headers and stretchers. The image displays a common joint misalignment that will always occur when the block's length equals twice its width.

Figure 3: This image further depicts the need for a standard spacer on interlocking blocks. The irregular block shape, which is not commercially available, is also laid in a herringbone fashion here. The "gearing" together of these blocks makes for consistently growing joint widths as the blocks are laid.

Conclusion: The examination of the laying modules, figures 2 and 3, illustrates the need to design blocks with a peripheral space of half a joint width from all block sides, which is shown in figure 1.

Check out the Construction Tolerances and Recommendations for Interlocking Concrete Pavements pdf by clicking here.